X-Ray and other high voltage power supplies (HVPS) often require an interface to an output cable that is convenient to connect and reconnect. Commonly this is accomplished by means of a plug and socket arrangement, where the socket is called a “cable well” or “well”. Inside the HVPS enclosure, the cable well looks like a cylinder attached to one side of the enclosure with its axis perpendicular to that side of the enclosure.
An example of an HVPS enclosure 10a according to the prior art is shown in FIG. 1.
The enclosure 10a may be a sheet metal box containing a quantity of insulating medium 15, such as transformer oil or oil. The end of the cable well 20 attached to a wall of the box 10a is the ground or low voltage end 21. The other, opposing end 22 is the high voltage end 22 of the cable well 20. The high voltage end 22 contains the actual high voltage terminal, which connects to the inner conductor or conductors of the cable of the cable well 20, and to the source of high voltage inside the box or tank 10a. The size of the cable well 20 is determined by its voltage rating. A higher voltage means a greater well length. The diameter D1 of the cable well 20 must be large enough to accommodate the outer diameter (OD) of the cable plus the outer diameter of the socket parts plus an adequate thickness of insulating material, commonly epoxy.
An illustrative embodiment of the present invention is designed for a HVPS with a voltage range from 100 to 200 kV and is used with a cable well 20 suitable for that voltage range, having a length L1 of 7 inches and a diameter D1 of 3 inches.
The high voltage terminal at the high voltage end 22 of the cable well 20 may comprise a trio of threaded studs or recessed threaded holes (not shown) to receive screws or studs. The high-voltage terminals are themselves quite small and if high voltage wires were attached to the terminals with no attempt at shielding, a well-known phenomenon known as “Field Enhancement” would cause a severe case of corona, almost certainly leading to high voltage arcing.
Field enhancement can be greatly reduced by increasing the size and radius of curvature of high voltage terminals. The required radius of curvature of a terminal is governed by the operating voltage, the insulating medium 15 and the distance D2 to the nearest point of low voltage or “Ground”. A ratio of 1.5:1 relating the distance D2 to ground to the radius of curvature of the high voltage terminal 30 provides a close to optimum reduction in field enhancement. For the voltage range of interest (i.e., 100 kV-200 kV) and for an insulating medium such as oil, 4.5 inches is an adequate but not extravagant distance D2 to ground. Applying the above-referenced ratio thereby requires a radius of curvature of 3 inches in the high voltage terminal 30. Thus, the high voltage end 22 of the cable well 20 would have to be surrounded by a conducting structure, commonly aluminum or brass, which would have an outside radius of curvature of at least 3 inches and would shield the much smaller terminals on the high voltage end 22 of the well 20 from ground.
A very common realization of this “Corona Shield” is shown in the high voltage anode terminal 30 of FIG. 1, which includes a toroid or donut shaped solid 31. The toroid 31 could also be machined on a lathe. Such a toroid 31 would have a cross sectional diameter D3 of 6 inches, which would provide the required radius of curvature of 3 inches. The donut hole or center of the toroid 31 would have a diameter D1 of 3 inches and would be plugged by a thin (relative to the diameters) disc 32, made of the same material of the toroid 31. Holes (not shown) in this disc 32 engage the three studs or threaded holes in the end 22 of the cable well 20 to make the high voltage connection. The overall outer diameter D4 of this shield 30 would be quite large at about 15 inches, which is five times the diameter D1 of the cable well 20. With another 4.5 inches of insulating space on each side of the toroid 31, corresponding to the distance D2 to ground, the minimum distance D5 between walls of the tank 10a would be 24 inches. This far exceeds the dimensions of any of the high voltage generating components in the tank 10a and is a tremendous waste of space, which greatly increases the cost of the tank 10a and cost of the oil medium 15 needed to fill the tank 10a. 
The problem with this “traditional” terminal having a circular cross-section is that the radius of curvature of 3 inches is maintained both outside and inside the toroid 31, thus resulting in a toroid 31 that has a diameter D3 of 6 inches, or twice the radius. The radius inside the toroid 31 is unnecessary since it is not looking at ground.
Thus, what is needed is a high voltage anode terminal that can meet the use requirements and reduce field enhancement and arcing, while also conserving physical space and reducing the overall cost of the high-voltage power supply.